There have been known fiber placement machines, commonly called fiber placement machines, for the application, by contact onto a layup tool, such as a male or female mold, of a wide band of several flat continuous fibers, ribbon-like, dry or impregnated with thermosetting or thermoplastic resin, in particular carbon fibers, consisting of a plurality of carbon filaments or threads.
These machines are used to produce preforms formed of several superposed plies, each ply being formed by laying up on a mold of one or several contiguous bands. In the case of a layup of fiber pre-impregnated with resin, the so-called pre-impregnated preform, is cured or polymerized by passing through an oven to obtain a composite material part. In the case of so-called dry fiber, not pre-impregnated with resins, comprising possibly a very small amount of so-called bonding resin, to impart tackiness to the fibers during the laying up, resin is injected or infused into the dry preform before the curing step.
These machines, such as described in the patent document WO2006/092514, typically comprise a fiber application head, a system of moving said fiber application head, fiber storage means, and fiber conveying means for conveying fibers from said storage means to the application head.
The fiber application head typically comprises an application roller, also called a compacting roller, intended to come into contact against the mold to apply the band, and means for guiding the fibers onto said application roller. The head generally further comprises a heating system for heating the fibers. The compacting roller presses the fiber band against the mold application surface, or against the fiber band or bands deposited beforehand, in order to facilitate the adhesion of the deposited bands between each other, and so that air trapped between the deposited bands is progressively discharged. The heating system heats the band of fibers, and/or the mold or the bands already applied upstream of the compacting roller, just before the compacting of the band, so as to at least soften the pre-impregnation resin or the binder resin, and thus promote the adhesion of the bands between each other.
The moving system ensures the movement of the application head in at least three directions perpendicular to each other. The moving system can be formed by a polyarticulated arm of the type of a standard six axes robot, arranged on the ground or mounted on a linear axis, with a wrist end to which the application head is fixed, or by a gantry type Cartesian robot, equipped with a wrist end carrying the application head.
In the case of fibers packaged in the form of spools, the fiber storing means typically comprises a creel or spool cabinet. The creel may be arranged on the ground close to the application head, for example in the case of a fixed standard robot, or can be mounted on an element of the moving system, for example on one of the carriages of a Cartesian robot or on the follower carriage sliding on the linear axis of the standard robot.
In order to ensure a substantially uniform compacting over the entire width of the band, the fiber placement head advantageously comprises a compacting roller able to adapt to the application surface, in particular to convex and/or concave application surfaces.
In the case of thermosetting resins, the pre-impregnated fibers are only heated to be softened, typically at temperatures of about 40° C. At these temperatures, the compacting roller is advantageously made of a so-called flexible material, elastically deformable, typically of an elastomeric material, so as to deform by matching the profile of the said surfaces.
In the case of thermoplastic resins, pre-impregnated fibers have to be heated to higher temperatures, at least up to the resin melting temperature, that is, of about 200° C. for nylon-type resins, and up to about 400° C. for PEEK-type resins. Because of the high heating temperatures, the fiber placement heads are equipped with metal compacting rollers, resistant to heat.
To adapt to the profile of the application surface, there have been proposed, particularly in the patent document U.S. Pat. No. 6,390,169, segmented metallic compacting rollers comprising several independent roller segments mounted side by side on a same axial rod, each segment being movable in said axial rod, perpendicularly the latter, independently, and being elastically biased against the application surface by elastic means, such as expansible bag systems.
Nevertheless, the structure of such segmented metallic rollers and their implementation proved to be complex.